When M&M’s are placed in water, the outer shell, which is made of sugar, dissolves. The sugar moves from a place of high concentration (the M&M) to a place of low concentration (the water away from the M&M). When the sugar shell dissolves and moves outward, it takes the layer of food dye with it. When more than one M&M is placed into a petri dish the colors do not mix because the concentration of sugar at the interface is approximately the same. Also, around the bottom of the M&M water appears cloudy because the sugar that is dissolved is more dense than the water, so it sinks.

Read More M&M Color Wheel